1. Field of the Invention
The present invention relates to a silver halide emulsion and a photographic light-sensitive material using the same and, more particularly, to a tabular silver halide grain emulsion having a high photographic sensitivity/granularity ratio and a photographic light-sensitive material using the same.
2. Description of the Related Art
Methods of manufacturing and using tabular silver halide grains (to be also referred to as simply "tabular grains" hereinafter) are disclosed in, e.g., U.S. Pat. Nos. 4,434,226, 4,439,520, 4,414,310, 4,433,048, 4,414,306, and 4,459,353. The tabular grain is known for its various advantages such as high sensitivity including an improvement in spectral sensitization efficiency obtained by a sensitizing dye, an improvement in a sensitivity/granularity relationship, an improvement in sharpness obtained by unique optical properties of the tabular grain, and an improvement in covering power.
In recent years, however, as the sensitivity of a silver halide color light-sensitive material has been increased and its small formatting has progressed, a strong demand has arisen for a color photographic light-sensitive material having high sensitivity and high image quality.
For this reason, a silver halide emulsion having higher sensitivity and better granularity is required. However, no conventional tabular silver halide emulsion can satisfy this requirement, and a demand has arisen for an emulsion having higher performance.
In the present invention, a technique of controlling dislocations to be formed in a center portion of a tabular silver halide grain is used in order to satisfy such requirement. A dislocation means a displacement in an atomic arrangement in a crystal lattice and is a kind of lattice defect. Since the origin of dislocations is not a thermodynamical one, no dislocations are included in crystals if the crystals are grown without being subjected to mechanical strain.
Dislocations in silver halide grains are described in, for example,:
1) C. R. Berry, J. Appl. Phys., 27, 636 (1956) PA1 2) C. R. Berry, D. C. Skilman, J. Appl. Phys., 35, 2165 (1964) PA1 3) J. F. Hamilton, Phot. Sci. Eng., 11, 57 (1967) PA1 4) T. Shiozawa, J. Soc. Phot. Sci. Jap. 34, 16 (1971) PA1 5) T. Shiozawa, J. Soc. Phot. Sci. Jap., 35, 213 (1972)
These references describe that dislocations in crystals can be observed by an X-ray diffraction method or a low-temperature transmission electron microscopic method and that various dislocations can be formed in crystals by giving strain to the crystals.
An influence of dislocations on photographic properties is described in G. C. Farnell, R. B. Flint, and J. B. Chanter, J. Phot. Sci., 13, 25 (1965). This reference describes that a formation position of a latent image nucleus in a large tabular silver bromide grain having a high aspect ratio and defects in the grain are in a close relationship.
J. W. Mitchell, J. Soc. Phot. Sci. Jap., 48, 191 (1985) describes a study of the tabular grain. According to this reference, dispersion of a latent image easily occurs in the tabular grain because the ratio of a surface area with respect to a volume is large in the tabular grain. The reference considers that in order to prevent this dispersion, electrons must be concentrated at the corner of the tabular grain, and preferably, at a singular point at the center of its major face to determine a latent image site.
JP-A-58-108526 ("JP-A" means unexamined published Japanese patent application) is an example of putting the above studies into practical use. JP-A-58-108526 discloses a tabular silver halide emulsion in which silver salt is coordinated in selected portions of parallel opposing (1,1,1) major faces of a tabular silver halide grain having an aspect ratio of 8 or more.
For example, an iodide concentration is controlled or a site director is adsorbed to major faces to coordinate AgCl in the corner or the central portion of a tabular grain.
This coordinated compound (epitaxy) of AgCl (or another silver salt such as AgSCN) is effective to limit the latent image site. On the other hand, since the coordinated compound has a high solubility and forms a mixed crystal with a host grain, it easily changes in subsequent steps (washing, chemical sensitization, coating, and incubation of a coated product). Therefore, it is difficult to maintain the performance of the compound.
Each of JP-A-63-220238 and JP-A-1-201649 discloses a tabular silver halide grain in which dislocations are formed on purpose. According to these patent specifications, tabular grains having dislocation lines are superior to those having no dislocation lines in photographic properties such as sensitivity and reciprocity. In addition, good sharpness and graininess can be imparted to a light-sensitive material by using these tabular grains. However, since a large number of dislocation lines are irregularly formed about the edges of these tabular grains, they are still unsatisfactory in terms of concentration of latent image formation sites.